Fundamental and clinically related studies are conducted on immune functions and cancer. Major advances in molecular immunology include demonstration of M-exons, a new class of structural gene sequences were discovered and shown to code for the transmembrane carboxy terminal membrane binding segment of IgM immunoglobulin micron heavy chains. Also the secretion or membrane-binding properties of all Ig heavy chain classes were found to be determined by different 3'-terminal coding sequences in their mRNAs as generated by alternate RNA processing pathways. Regulatory events for B cell maturation leading to IgM, IgG, and IgE antibody formation were investigated. After immunization (or booster) with diphtheria or tetanus, the cells forming IgM and IgG antibodies differ in cell surface features, particularly in terms of IgG presence (or absence). Furthermore, B cells with IgG surface molecules are susceptible to specific suppression (tolerance). T lymphoid cell mechanisms and their regulation were studied in several systems. 1. Cytotoxic cells were found to have Lyt 2,3 alloantigens (or close-by membrane components) associated with the binding step of the cytolytic process. Antisera have been developed to isolate the relevant cell membrane molecules. 2. Soluble cytotoxic factors for NK target cells were obtained from stimulated normal murine or human lymphocytes and found to differ from Granger's lymphotoxin. Suppression of immune functions by certain neoplastic diseases (head and neck epidermal cancer, bladder transitional cell cancer) was shown to involve monocyte activation. Soluble suppressor factors were identified. In 30% of head and neck cancer patients, defective T(responding) cells were found. In preliminary studies, activity could be restored by soluble T cell factors.